How long has he been using steroids without a break, and how old is he? If it's been a really long time, then he's likely a strong candidate for TRT prescribed through a doctor.
One thing to remember is that, as far as his health is concerned, it really doesn't matter if he's lifting or not. It's not like steroids are more dangerous if you don't lift. So you should ask yourself if it would bother you if he was using steroids and actually going to the gym.
It also sounds like you don't know what he's actually taking. It could be, essentially, self prescribed TRT if he's just taking 2 1ml shots per week. Doesn't seem like that's clear.
I really just wanted to throw some things out there for you to consider to help you decide what path to take. I would personally encourage the TRT through a doctor route. If it really is something along the lines of simply being addicted to injections, that could be a safer way to feed that addiction. It would also be a better option than stopping altogether. If he stops, he's going to crash his hormone levels. Which means he would go through a shitty mental experience. TRT would help avoid this. So, he could run TRT while he's not lifting, and if he so chooses and you're ok with it, run more gear while he is actually going to the gym.
Hope this helps!